Canon's announcement of an affordable EF 40mm f/2.8 sent lots of EOS shooters to their retailer of choice to pre-order the lens as quick as they could. Unfortunately, some have encountered a problem with the focus system that Canon recently acknowledged with a service advisory. It seems that putting pressure on the lens barrel while it's attached to the camera - be it from a jostle in your camera bag or just putting the lens cap in place - can cause the auto focus to stop functioning.
In these instances, taking the lens off and re-attaching it or pulling the battery out will straighten things out - until it happens again. It seems there's no damage occuring to the lens in these cases. Canon will offer a firmware update in late August 2012 to fix the issue. Until then, those early adopters will have to endure with a finicky lens.
Be on the lookout for the firmware update later this month. For now, head over to Canon's service website for more information on the issue.